Method of and system for reducing secondary pressure pulses in operation of pneumatic sound source in water

ABSTRACT

The specification discloses a device employed in a pneumatic sound source for controlling the release of gas through a chamber port to minimize secondary pressure pulses. In the embodiment disclosed, the device comprises an enlarged portion coupled to a release valve by way of a smaller supporting member, both of which pass through the port as the valve moves to its porting position. As the valve initially moves toward its porting position, gas pressure is rapidly released from the chamber through the port and into the water to generate a primary pressure pulse. As the enlarged portion of the gas control device passes into the port, the rate of flow of gas through the port is decreased. Upon passage of the enlarged portion out of and beyond the port, additional gas is allowed to flow through the port to dampen bubble oscillation to minimize secondary pressure pulses.

United States Patent 1191 Huffhines I45] July 17, 1973 {75] Inventor: Donald F. Huffhines, Richardson.

Tex.

[73] Assignee: Mobile Oil Corporation, New York,

[22] Filed: May 23, 1972 [211 App]. No: 256,197

Related US. Application Data [63] Continuation of Ser. No. 31,103, April 23, 1970,

OTHER PUBLICATIONS Kramer et al., Seismic Energy Sources Handbook of AIR 39 COMPRESSOR sWFTcHiATG CIRCUITRY Primary lxamin0rl3enjamin A. Borchelt Assistant Examiner-N. Moskowitv. Attorney-William J. Schcrback et al.

57 ABSTRACT The specification discloses a device employed in a pneumatic sound source for controlling the release of gas through a chamber port to minimize secondary pressure pulses. In the embodiment disclosed, the device comprises an enlarged portion coupled to a release valve by way of a smaller supporting member, both of which pass through the port as the valve moves to its porting position. As the valve initially moves toward its porting position, gas pressure is rapidly released from the chamber through the port and into the water to generate a primary pressure pulse. As the enlarged portion of the gas control device passes into the port, the rate of flow of gas through the port is decreased. Upon passage of the enlarged portion out of and beyond the port, additional gas is allowed to flow through the port to dampen bubble oscillation to minimize secondary pressure pulses.

10 Claims, 10 Drawing Figures Pat ented July 17, 1973 5 Sheets-Sheet 1 FIG.

AIR COMPRESSOR INVEINTOR DONAL D F. HUFFHINES Patented July 17, 1973 3,746,123

5 Sheets-Sheet 2 FIG. 2

INVENTOR DONALD F. HUFFHINES Patented July 17, 1973 INVENTOR DONALD F HUFFHINES Patented July 17, 1973 3,746,123

5 Sheets-Sheet 4 0 souRcE WITH DEBUBBLER AT 35 500psi HYDROPHONE AT 35' I2'AWAY 500psi F I G 6 63 CHANGE IN CHAMBER PRESSURE WITH DEBUBBLER 20psi 0 SOURCE WITHOUT DEBUBBLER AT '35 '-500psI HYDROPHONE AT 35' I2" AWAY 500psi Fl 6. 8

CHANGE IN CHAMBER PRESSURE WITHOUT DEBUBBLER 20 INVENTOR DONALD F. HUFFHINES METHOD OF AND SYSTEM FOR REDUCING SECONDARY PRESSURE PULSES IN OPERATION OF PNEUMATIC SOUND SOURCE IN WATER This is a continuation, of application Ser. No. 31,103, filed Apr. 23, 1970 now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a method of and system for reducing secondary pressure pulses resulting from the operation of a pneumatic acoustic source in water.

In recent years the seismic industry has been using pneumatic sound sources to carry out marine seismic operations. These sources rapidly release gas under pressure into the water to generate a pressure pulse. Secondary pressure pulses of relatively large magnitude however are generated from extreme oscillation of the resulting bubble. These secondary pressure pulses are objectionable in that they are reflected from the subsurface interfaces and are recorded together with the reflections from the primary pressure pulse. Data processing operations have been carried out to reduce the effect of the secondary pressure pulses on the records obtained. Such processing operations however have not proved to be completely satisfactory and moreover are expensive.

A need has existed for a simple device and method for reducing the secondary pressure pulses but which do not affect the primary pressure pulse nor the efficiency or operation of the sources or associated equipment.

SUMMARY OF THE INVENTION In accordance with the present invention, a simplitied and effective method and system are provided for operating a pneumatic sound source for significantly reducing the secondary pressure pulses with a minimum effect on the primary pressure pulse. In carrying out the method, the opening of a container in a body of water is sealed and the container is pressurized with gas. The size of the opening is rapidly increased to rapidly release pressurized gas from the container into the water to generate a primary pressure pulse in water. The size of the opening is reduced and, following the formation of a bubble, the size of the opening is increased to allow additional gas from the container to flow into the bubble to reduce secondary pressure pulses.

In the pneumatic sound source disclosed, a chamber is provided for receiving gas and holding gas under pressure to be released into the water by way of a chamber port. Movable valve means is supported for movement between a closed position and a porting position. In addition, means is provided for maintaining the valve means in the closed position for confining pressurized gas in the chamber and for allowing the valve means to move to its porting position. The valve means, upon movement from its closed position to its porting position, opens the port to allow gas under pressure initially to be released rapidly through the port and into the water to generate a primary pressure pulse in water. Next, it reduces the size of the gas flow path through the port to decrease the rate of flow of gas through the port. The valve means then increases the opening through the port to allow additional gas to flow through the port to minimize secondary pressure pulses.

In the preferred embodiment, the valve means comprises a pressure-retaining means for sealing the port when the valve is in its closed position. Extending from the pressure-retaining means is a gas release control means supported to follow the pressure-retaining means and to pass through and beyond the port upon movement of the valve means to its, porting position. The gas release control means comprises an enlarged portion spaced from the pressure-retaining means. As this enlarged portion moves into the port, it reduces the size of the gas flow path through the port and then allows the size of the gas flow path through the port to increase as it moves out of and beyond the port.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. ll illustrates a pneumatic sound source employed in marine seismic surveying operations;

FIG. 2 illustrates in detail the internal and external structure of the source of FIG. 1;

FIG. 3 is an enlarged partial cross section of the device of the present invention used in the source to minimize secondary pressure pulses;

FIG. 4 is a cross section through lines 44 of FIG.

FIGS. S8 are traces useful in understanding the present invention;

FIG. 9 is an enlarged cross section of a portion of the source with its valve partially open; and

FIG. 10 is an enlarged section of a portion of the throat of the port of the source.

DESCRIPTION OF THE OPERATION OF THE PNEUMATIC SOUND SOURCE Referring now to FIG. 1, an acoustic source 20 is shown supported in water from a boat 21 by a cable 22. As can be seen in FIG. 2, the acoustic source comprises enclosing wall structure 24 forming a pressure chamber 25 which has an outlet port 26. A quick-opening valve 27 of ferromagnetic material is provided for sealing the port and then rapidly opening the port to generate a pressure pulse in the water. A spring 28 is provided for moving the valve to its closed or sealing position. An electromagnet comprising an electrical coil 29 and a ferromagnetic core 30 is energized to form a magnetic holding force for holding the valve in its closed position. Electrical current is applied to the coil from a d-c power supply 32 shown in FIG. I in the enclosed dotted box 33 located on the boat 21. Current is applied to the coil from the power supply 32 by way of a normally closed switch included in the switching circuitry 34 and electrical leads 35a and 35!) which are coupled to the source.

When the valve is in its closed position, the pressure chamber 25 is pressurized with air supplied by air compressor 37. A seal 38 maintains a pressure seal between the core 30 and the valve 27 to seal the pressurized air in the chamber 25. Air compressor 37 is coupled to the acoustic source by conduit 39, normally open valve 40, and flexible conduit 42, the latter of which extends to the chamber 25. After pressure in the chamber 25 becomes equal to that in the air compressor reservoir (not shown), the flow of air to the source stops. An acoustic pulse is generated by interrupting the flow of current through the coil 29. When this occurs, the magnetic holding force decreases and the high gas pressure in the chamber 25 rapidly moves the valve 27 to its open or porting position to the right of the edges 43a of the venting ports 43. The pressurized gas rapidly flows through the chamber port 26 and through venting ports 43 into the water to generate a pressure pulse or acoustic pulse in the water. Interruption of the current through the coil 29 is carried out by opening the switch provided in switching circuitry 34. A timer 44 is provided to control the switching circuitry 34, by way of conductor 44b, to repetitively generate pressure pulses, for example, at a repetition rate of five acoustic pulses per minute. In actual seismic surveying operations, four sources 20 may be employed, all supplied with air from a single compressor system. These sources may be located at a depth of about 40 feet below the surface of the water and fired simultaneously to enhance the acoustic energy produced.

PREFERRED EMBODIMENT OF THE INVENTION The source of FIG. 2 is similar to that disclosed in copending application Ser. No. 14,904 filed on Feb. 27, 1970, by George B. Loper, now US. Pat. No. 3,612,210. The source disclosed in said patent, however, has been modified in accordance with the present invention to provide a gas release control device 50 for reducing secondary pressure pulses. In addition, the throat of the port 26 has been rounded at its edge formed by the structure which holds the seal 38. The amount of rounding is shown in FIG. 10.

Referring to FIG. 3, the device 50 is formed of three membersan orifice plate 51, a spacer 52 of a holddown bolt 53, and a cone support 54. The orifice plate 51 comprises an enlarged portion 51a which is spaced from and coupled to the valve 27. This portion flares outward from a small neck or base 51b in a direction away from the valve 27. The maximum diameter of the flared portion 51a is slightly smaller than the minimum diameter of the port 26. The neck 51b, spacer 52, and neck 54a of the cone support 54 form a smalldiametered portion or stem which spaces the enlarged portion 5 1a from the valve 27. The hold-down bolt 53 has one end 53a inserted through the cone support 54 and threaded into the valve 27. The other end 53b is threaded into the neck or base of the orifice plate 51 whereby the device 50 is an integral device securely fastened to the valve 27. Upon movement of the valve 27 to its porting position, the device 50, including the enlarged portion 51a, follows the valve 27 and is moved completely through and beyond the port 26. This arrangement and operation significantly reduces secondary pressure pulses with little effect on the primary pressure pulse.

Reference now is made to FIGS. 5 and 6 which show the pressure changes measured in the water outside the chamber 25 and within the chamber 25, respectively,

employing thesource of FIG. 2 incorporating the device and having the throat of its port 26 rounded. In FIG. 5, pressure increases in the downward direction. Prior to firing, the chamber 25 was pressurized to 500 pounds per square inch. Following de-encrgization of the coil 29, the valve 27 rapidly is moved away from the core 30 to open the port 26. Gas pressure then is rapidly released from the chamber through the port 26 and then into the water to generate a pressure pulse of large amplitude. This pulse is illustrated at 60 in FIG. 5. Its relative amplitude is 156. The pressure drop within the chamber during the high rate of discharge of the gas is illustrated between points 61 and 62 in FIG. 6. The cone-shaped supporting structure 54 and the smalldiametered stem portion comprising neck 51b, spacer 52, and neck 54a have little effect upon the discharge of gas through the port.

As the enlarged portion 51a of the device 50 passes within the port, however, the rate of discharge of gas through the port is decreased. This decrease of the rate of discharge of gas is illustrated between points 62 and 63 in FIG. 6. As the enlarged portion 51a passes through and beyond the port, additional air within the chamber 25 is allowed to flow through the port and into the bubble formed to dampen bubble oscillation and hence to minimize secondary pressure pulses. The rate of discharge of the gas through the port after the enlarged portion 51a is moved through and out of the port is shown between points 63 and 64 in FIG. 6. This rate of discharge is less than the rate of discharge illustrated between points 61 and 62 but greater than that illustrated between points 62 and 63. Referring to FIG. 5, the only secondary pressure pulse produced above hydrostatic pressure (the zero level) is shown at 66. Its relative amplitude is only fourmuch less than the relative amplitude of the primary pressure pulse 60.

FIGS. 7 and 8 illustrate traces obtained from operation of the source without the device so. In addition, the edge of the port 26, formed by the seal supporting structure, was square rather than rounded as will be described subsequently. FIG. 7 illustrates pressure changes measured in the water, while FIG. 8 illustrates pressure changes measured in the chamber. In FIG. 7, pressure increases in the downward direction. As can be seen from FIG. 8, the pressure within the chamber drops rapidly as the valve 27 moves toward its porting position. In FIG. 7, the primary pressure pulse is shown at 70. It has a relative amplitude of l65only slightly greater than the relative amplitude of the primary pressure pulse 60 (FIG. 5) produced with the source of FIG. 2. Severe bubble oscillation, however, has occurred and a large pressure drop was recorded at 71, with a resulting strong secondary pressure pulse being produced at 72. Further bubble oscillation has resulted in subsequent secondary pressure pulses of reduced amplitude being produced, one being identified at 73. The relative amplitude of pulse 72 is I 12, while the relative amplitude of pulse 73 is 34.

Upon analysis of the curves shown in FIGS. 5, 6, and 7, it appears that the additional air, which flows through the port 26 when the enlarged portion 51a of device 50 passes out and beyond the port, flows into the bubble when its pressure otherwise would drop to a very low level below hydrostatic pressure (at 71 in FIG. 7) immediately following the primary pressure pulse. The additional air supplied into the bubble at this time significantly minimizes secondary pressure pulses. There is some pressure variation immediately following the primary pressure pulse 60 as shown in FIG. 5. However, it is of low amplitude below hydrostatic pressure and does not produce the undesired effect.

The reduction in secondary pressure pulses was due primarily to the use of the device 50. The purpose in rounding the edge of the throat of the port 26was to obtain a more gradual change in the rate of discharge of additional gas through the port as the enlarged portion 51a of device 50 passes through the port. Rounding of the edge also allowed the additional gas to begin flowing at an earlier time. In obtaining the traces of FIGS. 5-8, the chamber 25 was pressurized to 500 pounds per square inch from a source of gas pressure.

tending through an aperture in the plate and threaded into the valve 27.

In the source tested to obtain the traces of FIGS. 7 and 8, the seal disclosed in FIG. 10 was employed, but with the structure 84 having the square edge 84a. The device 50 was not used, but the structure disclosed in dotted form in FIG. 9 was employed to hold the plate 145 in place. This structure consisted of a truncated, cone-shaped washer 150 and a bolt I51 inserted through the washer 150 and plate 145 and threaded to the valve 27. A pin 152 and a wire member 153 coupled to the pin and to the bolt 151 were employed to prevent the washer from rotating.

The source employed to obtain the traces of FIGS. 5-8 has a chamber volume of about 0.9 cubic foot. When operated to generate acoustic pulses, the chamber was pressurized to 500 pounds per square inch above atmospheric pressure. The source had four vents 43. The distance between the vent edges 43a and the plane of the core surface 30a was about 1 inch. The length of the vents 43 along the axis of the source was about 245/16 inches. The outside diameter of the valve 27 was 14.080 inches.

The valve 40 is a manually controlled valve which is open continually during shooting operations and cut off when the source is not in use. The internal diameter of conduit 42 is 13/32 inch. This size is sufficient to allow the chamber 25 to become pressurized to 500 pounds per square inch within 12 seconds (firing rate of five pulses per minute) but small enough whereby air from the compressor system does not prevent the retract spring 28 from closing the valve 27 after firing during each cycle. In operation of the source, after firing, the coil 29 is energized during each cycle prior to the return of the valve 27 to its closed position whereby the valve is held closed when it reaches its closed position and the cycle is repeated.

What is claimed is:

1. An acoustic source for generating pressure pulses in water for exploratory purposes, comprising:

a chamber for receiving gas and holding gas under pressure to be released into the water for the generation of a primary pressure pulse in water,

said chamber being formed of rigid wall structure and having a single outlet port,

movable valve means supported for movement between a closed position and a porting position, relative to said single outlet port,

means for maintaining said valve means in said closed position for confining pressurized gas in said chamber and for allowing said valve means to move to said porting position, and

an enlarged member attached to and spaced from said valve means, said enlarged member passing through said outlet port upon movement of said valve means to said porting position to decrease the rate of flow of gas through said port and to thereafter allow additional gas from said chamber to flow through said port into the bubble formed following the initial release of gas pressure to minimize secondary pressure pulses.

2. The acoustic source of claim 1 wherein said valve means comprises:

first, second, and third portions, including said enlarged member, supported for movement relative to said port,

said second portion being located intermediate said first and third portions,

said second and third portions moving sequentially past a predetermined point relative to said port upon movement of said valve means to said porting position,

said first portion maintaining said port closed when said valve means is in said closed position,

said second and third portions controlling the size of the gas flow path through said port as said valve means moves toward said porting position,

said second portion allowing a relatively large gas flow path through said port to allow gas under pressure to be released rapidly through said port and into the water to generate a primary pressure pulse,

said third portion reducing the size of the gas flow path through said port to decrease the rate of flow of gas through said port, and

said third portion, upon movement past said predetermined point, allowing said gas flow path through said port again to increase in size to allow addi* tional gas to flow through said port into the bubble formed to minimize secondary pressure pulses.

3. The acoustic source of claim 2 wherein:

said second portion is smaller in cross section than said third portion, and

said second and third portions are supported to move sequentially through said port and beyond upon movement of said valve means to said porting position.

4. An acoustic source for generating pressure pulses in water for exploratory purposes, comprising:

a single chamber for receiving gas and holding gas under pressure to be released into the water for the generation of a primary pressure pulse in water,

said chamber being formed of rigid wall structure and having an outlet port,

movable valve means supported for movement between a closed position and a porting position,

said valve means comprising a pressure-retaining means and a gas release control means extending from said pressure-retaining means and supported to follow said pressure-retaining means upon movement of said valve means to said porting position,

said pressure-retaining means sealing said port when said valve means is in said closed position,

said gas release control means increasing in crosssectional size in a direction away from said pressure-retaining means,

said gas release control means being located to pass through and beyond said port upon movement of said valve means to said porting position, and

means for maintaining said valve means in said closed position for confining pressurized gas in said chamber and for allowing said valve means to move to said porting position,

said valve means, upon movement away from said closed position toward said porting position, allow ing gas under pressure initially to be released rapidly through said port and into the water to generate a pressure pulse in water,

said gas release control means, upon movement through said port, reducing the size of the gas flow path through said port and then allowing the size of the gas flow path through said port to increase to After the chamber was pressurized, the valve 40 was closed and the source then fired.

It can now be understood that the present invention significantly minimizes secondary pressure pulses with little or no effect upon the primary pressure pulse. Moreover, the device 50 is simple to build and install. Furthermore, the use of the device 50 does not decrease the firing rate of the source nor does it require additional gas to be injected into the chamber nor the use of a larger air compressor. It allows the gas pressure injected within the chamber 25 during each cycle to be more effectively and efficiently used not only to generate a strong primary pressure pulse but to minimize secondary pressure pulses.

Referring again to FIG. 3, the actual dimensions in inches of the device 50 as well as the amount of taper of the orifice plate 51 and the support 54 are set forth in FIG. 3. The enlarged portion 51a of member 51 and member 54 both are circular in cross section through the axis of the device 50 with the enlarged portion 510 having a maximum diameter of 4.937 inches. The minimum diameter of the port or opening 26 is 5 inches. Members 51,54 and the hold-down bolt 53 were machined from stainless steel. A pin 80 inserted into an aperture in member 54 and into the valve 27 prevents the member 54 and hence the device 50 from turning. Set screws 81 and 82 provide additional coupling support of members 51 and 54 to the hold-down bolt 53. The cross section of the spacer 52 is shown in FIG. 4. The flat surfaces 52a were machined to provide gripping surfaces to facilitate assembly. Flat surfaces 51b also were machined on both sides of the neck 51b to provide gripping surfaces. Except for the material removed to form these flat surfaces, the neck 51b is circular in cross section. The stem portion comprising neck 51! spacer 52, and neck 54a has a diameter of 1.25 inches. The maximum length of the device 50 from the edge 50a to edge 50b is of the order of 3% inches. The maximum distance which the valve 27 travels from its closed position to its porting position when the source is in water is of the order of 3-9/16 inches. Upon movement of the valve 27 to its porting position, the device 50, including its left edge 50a, is moved through the port 26 and to the right of the plane of the core surface a (FIG. 9). In this position, the clearance between the edge 50a of the device 50 and the plane of the core surface 30a is about 7/16 inch.

As indicated above, the amount of rounding of the throat of the port 26 is shown in FIG. 10. The portion which was rounded was the edge of the structure 84 employed to hold the seal. The portion which was removed is illustrated in dotted form at 84a. Additional information on the shape and dimensions of the structure forming the port or orifice 26 is given on the draw mg.

Referring again to FIGS. 1 and 2, there will be described more of the mechanical details of the source and equipment. Cable 22 is coupled to a harness 100 which in turn is coupled to nose member 101 and vertical tail fin 102. Also coupled to the harness is a strain cable 103 which extends to the boat 21 and is securely affixed to the boat at 104. The cable 22 is supported at the end of the boat by a reel 105 and winch 106. A motor and reel system 107 is employed to reel the cable in and out to raise and lower the source, respectively. The conduit 42, electrical leads a and 35b, and cable 103 are bound together by tape to form a flexible and lightweight conduit 108 which is let out and pulled in by hand.

At the source, the conduit 42 extends through tubing 1 10 coupled to the harness and then to an inlet 111 which leads to the pressure chamber 25. The electrical leads 35a and 35b extend through tube 112 coupled to the harness and then through smaller tubes 113 and 1 14 coupled to the harness and to the source. The electrical leads 35a and 35b then extend to a terminal box 115 where they are connected to the two ends of the electrical coil 29. The electrical coil 29 is secured in a slot 116 formed in the core 30. An encapsulating epoxy may be used to secure the coil in the slot.

Coupled to the backend of the valve 27 by machine screws 118 is a cylinder 119 which guides the valve 27 in its movement and also supports one end of the retract spring 28. Cylinder 119 is supported for movement by bearing 120 located in a cylinder 121. Cylinder 121 is coupled to the core 30 by an arrangement including annular plate 122 and cylinder 123 in which the venting ports 43 are formed. Cylinder 123 is welded to annular plate 122 and is coupled to the core 30 by machine screws 124. The dimensions of the valve 27 and the skirt portion of the cylinder 123 extending from the core 30 are such that there is a lack of fluid seal, allowing fluid flow clearance between the outer periphery of the valve and the interior surface of the skirt portion.

The other end of the spring 28 is supported in an annular-shaped member formed by cylinder 126 coupled to cylinder 127 by way of spokes 128. Cylinder 127 in turn is threaded into cylinder 121. Secured to the exterior of cylinder 121 is an annular member 130. A truncated, cone-shaped member 131 is coupled to the annular plate 122 and annular member for additional support for the backend portion of the source. A plate 132 is coupled to the annular member 130 by way of machine screws 133. Coupled to the plate 132 are the fins 102, 135, and 136.

The valve 27 is slowed and stopped at the end of its opening movement by water located in the container formed by plate 122 and the backend of cylinder 123. The outside diameter of valve 27 is slightly smaller than the interior diameter of cylinder 123 as indicated above, whereby water may flow between these members. As the valve moves within this container, water is squeezed between the outside surface of the valve and the inside surface of the container to decelerate the valve. Water within cylinder 119 may flow by way of apertures 137 extending through cylinder 119 and by way of aperture 138 extending through plate 132.

Referring to FIG. 10, the seal 38 comprises a stainless steel ring 139 biased by a resilient elastomer O-ring 140 located in a slot 141. This slot is formed by metal holding rings 84 and 142 secured to the core 30 by bolts illustrated at 143. A plurality of spaced, radially extending channels 144 extend to the slot 141 whereby pressurized air from the chamber 25 is applied to the slot 141 for effecting a seal between the elastomer O-ring 140, the walls of the slot 141, and the metal seal 38; and between the metal seal 38 and a stainless steel plate 145 (FIG. 9) secured to valve 27. Resilient O-ring 146 located in slot 147 provides a seal between ring 84 and core structure 30. This seal arrangement is similar to that described in US. Pat. No. 3,506,085.

In the source of FIG. 2, the steel plate 145 is held in place by the cone support 54 and hold-down bolt 53 exallow additional gas to flow through said port to minimize secondary pressure pulses.

5. An acoustic source for generating pressure pulses in water for exploratory purposes, comprising:

a chamber for receiving gas and holding gas tinder pressure to be released into the water for the generation of a primary pressure pulse in water,

said chamber being formed of rigid wall structure and having an outlet port,

movable valve means supported for movement between a closed position and a porting position,

said valve means comprising:

a. a pressure-retaining means,

b. a stem portion extending from said pressureretaining means and having a cross section much smaller than the cross-sectional size of said port, and

c. a flared portion coupled to said stem portion and which increases in cross section in a direction away from said pressure-retaining means to a size much larger than the cross section of said stem portion,

said pressure-retaining-means sealing said port when said valve means is in said closed position,

said stem and flared portions being located sequentially to pass through and beyond said port upon movement of said valve means to said porting position, and

means for maintaining said valve means in said closed position for confining pressurized gas in said chamber and for allowing pressurized gas in said chamber to move said valve means to said porting position,

said valve means upon movement away from said closed position toward said porting position, allowing gas under pressure to be released rapidly through said port and into the water to generate a pressure pulse in water,

the rapid release of gas pressure intothe water to generate the pressure pulse resulting in the formation of a bubble,

said flared portion, upon movement through said port, reducing the size of the gas flow path through said port and then allowing the size of the gas flow path through said port to increase to allow additional gas to flow through said port into the resulting bubble formed to minimize secondary pressure pulses.

6. In an acoustic source for generating pressure pulses in water for exploratory purposes, comprising:

a chamber for receiving gas and holding gas under pressure to be released for the generation of a pres sure pulse in water,

said chamber being formed of rigid wall structure and having an outlet port, 1

movable valve means supported for movement between a closed position and a porting position for closing and opening said outlet port, respectively,

means for maintaining said valve means in its closed position for confining pressurized gas in said chamber and for allowing pressurized gas in said chamber to move said valve means to said porting position for releasing pressurized gas rapidly from said chamber by way of said port into the water to generate a pressure pulse in water,

the rapid release of pressurized gas into the water to generate the pressure pulse resulting in the formation of a bubble, and

means for returning said valve means to said closed position,

the combination therewith of:

gas release control means coupled to said valve means and supported to extend therefrom for controlling the release of gas through said port to re duce secondary pressure pulses,

said gas release control means having a larger portion in cross section spaced from said valve means and a smaller portion in cross section located between said larger portion and said valve means,

said valve means, upon movement to said porting position, causing first said smaller portion and then said larger portion to move through and beyond said port,

said larger portion, upon movement within said port, decreasing the rate of gas flow through said port and then allowing the rate of gas flow through said port to be increased as it moves beyond said port whereby additional gas is allowed to flow through said port into the bubble to minimize secondary pressure pulses.

7. In an acoustic source for generating acoustic pulses in water for marine seismic exploration operations, comprising:

a chamber for receiving gas and holding gas under pressure to be released into the water for the generation of a pressure pulse,

said chamber being formed of rigid wall structure to be immersed in water,

said chamber having a first end and an outlet port,

annularly shaped structure coupled to said wall structure at a position spaced from said first end,

said outlet port extending through said annularly shaped structure,

movable valve means formed of structure supported for movement between a closed position adjacent said annularly shaped structure and an open position for closing and opening said outlet port, re spectively,

said valve means preventing the release of pressun ized gas from said chamber when said valve means is in said closed position,

an electrical coil associated with said annularly shaped structure to form an electromagnet:

a. for forming a magnetic holding force when electric current is applied to said coil for application of said force to said structure of said valve means for holding said valve means in said closed position against pressurized gas in said chamber, and

b. responsive to decreased current flow for decreasing said holding force to allow pressurized gas in said chamber to move said valve means to said open position to release pressurized gas rapidly from said chamber by way of said outlet port for flow into the water to generate a pressure pulse,

the rapid release of pressurized gas into the water to generate said pressure pulse resulting in the formation of a bubble, and

means for returning said valve means to said closed position,

the combination therewith of:

gas release control means coupled to said valve means for controlling the release of gas through said port to reduce secondary pressure pulses,

said gas release control means comprising:

a stem portion extending from said valve means and having a cross section much smaller than the crosssectional size of said port, and

a flared portion coupled to said stem portion and which increases in cross section in a direction away from said valve means to a size much larger than the cross section of said stem portion,

said stern and flared portions being located sequentially to pass through and beyond said port upon movement of said valve means to said porting position,

said flared portion, upon movement within said port, reducing the size of the gas flow path through said port and then allowing the size of the gas flow path through said port to increase as it moves beyond said port to allow additional gas to flow through said port into the bubble formed to minimize secondary pressure pulses.

8. In an acoustic source for generating pressure pulses in water for exploratory purposes, comprising:

a chamber for receiving gas and holding gas under pressure to be released into the water for the generation of a pressure pulse,

said chamber having an axial opening smaller in cross section than the cross-sectional area of said chamber in a plane perpendicular to the axis thereof,

structure having lateral vent means formed therethrough,

valve means supported for movement within said structure between a closed position adjacent said opening and a porting position spaced from said opening,

means for maintaining said valve means in said closed position for confining pressurized gas in said chamber and for allowing pressurized gas in said chamber to move said valve means to said porting position,

the combination therewith of:

gas release control means coupled to said valve means and supported to extend therefrom for controlling the release of gas to reduce secondary pressure pulses,

said gas release control means having a larger portion in cross section spaced from said valve means and a smaller portion in cross section located between said larger portion and said valve means,

said valve means, upon movement to said porting position, causing first said smaller portion and then said larger portion to move through and beyond said opening,

said valve means, upon movement away from said closed position toward said porting position, allowing gas under pressure initially to be released rapidly through said opening and through said vent means into the water to generate a pressure pulse in water,

the rapid release of pressurized gas into the water to generate the pressure pulse resulting in the formation of a bubble, and

said larger portion, upon movement within said opening, decreasing the rate of gas flow through said opening and then allowing the rate of gas flow through said opening to be increased as it moves beyond said opening whereby additional gas is allowed to flow through said opening and through said vent means into the bubble to minimize secondary pressure pulses.

9. The acoustic source of claim 8 wherein:

said opening is formed through a member having a surface facing said valve means, 7

said valve means having a surface facing said surface of said member and movable adjacent thereto upon movement of said valve means to said closed position,

said member having rounded edges formed between said opening and said surface of said member facing said valve means.

10. An acoustic source for generating acoustic pressure pulses in water for exploratory purposes while reducing secondary pressure pulses which occur following release of high pressure gas into water, comprising:

a chamber for receiving gas and holding gas under pressure to be released into the water for the generation of a primary pressure pulse in water, said chamber being formed of rigid wall structure and having an outlet port,

a valve member normally closing said outlet port and being movable away from said outlet port to an open position, and w an enlarged member attached to and spaced from said valve member, said enlarged member passing through said outlet port upon movement of said valve member to said open position to decrease the rate of flow of gas through said port and to thereafter allow more of said gas to flow through said port into the bubble formed following the initial release of gas pressure to minimize secondary pressure pulses. 

1. An acoustic source for generating pressure pulses in water for exploratory purposes, comprising: a chamber for receiving gas and holding gas under pressure to be released into the water for the generation of a primary pressure pulse in water, said chamber being formed of rigid wall structure and having a single outlet port, movable valve means supported for movement between a closed position and a porting position, relative to said single outlet port, means for maintaining said valve means in said closed position for confining pressurized gas in said chamber and for allowing said valve means to move to said porting position, and an enlarged member attached to and spaced from said valve means, said enlarged member passing through said outlet port upon movement of said valve means to said porting position to decrease the rate of flow of gas through said port and to thereafter allow additional gas from said chamber to flow through said port into the bubble formed following the initial release of gas pressure to minimize secondary pressure pulses.
 2. The acoustic source of claim 1 wherein said valve means comprises: first, second, and third portions, including said enlarged member, supported for movement relative to said port, said second portion being located intermediate said first and third portions, said second and third portions moving sequentially past a predetermined point relative to said port upon movement of said valve means to said porting position, said first portion maintaining said port closed when said valve means is in said closed position, said second and third portions controlling the size of the gas flow path through said port as said valve means moves toward said porting position, said second portion allowing a relatively large gas flow path through said port to allow gas under pressure to be released rapidly through said port and into the water to generate a primary pressure pulse, said third portion reducing the size of the gas flow path through said port to decrease the rate of flow of gas through said port, and said third portion, upon movement past said predetermined point, allowing said gas flow path through said port again to increase in size to allow additional gas to flow through said port into the bubble formed to minimize secondary pressure pulses.
 3. The acoustic source of claim 2 wherein: said second portion is smaller in cross section than said third portion, and said second and third portions are supported to move sequentially through said port and beyond upon movement of said valve means to said porting position.
 4. An acoustic source for generating pressure pulses in water for exploratory purposes, comprising: a single chamber for receiving gas and holding gas under pressure to be released into the water for the generation of a primary pressure pulse in water, said chamber being formed of rigid wall structure and having an outlet port, movable valve means supported for movement between a closed position and a porting position, said valve means comprising a pressure-retaining means and a gas release control means extending from said pressure-retaining means and supported to follow said pressure-retaining means upon movement of said valve means to said porting position, said pressure-retaining means sealing said port when said valve means is in said closed position, said gas release control means increasing in cross-sectional size in a direction away from said pressure-retaining means, said gas release control means being located to pass through and beyond said port upon movement of said valve means to said porting position, and means for maintaining said valve means in said closed position for confining pressurized gas in said chamber and for allowing said valve means to move to said porting position, said valve means, upon movement away from said closed position toward said porting position, allowing gas under pressure initially to be released rapidly through said port and into the water to generate a pressure pulse in water, said gas release control means, upon movement through said port, reducing the size of the gas flow path through said port and then allowing the size of the gas flow path through said port to increase to allow additional gas to flow through said port to minimize secondary pressure pulses.
 5. An acoustic source for generating pressure pulses in water for exploratory purposes, comprising: a chamber for receiving gas and holding gas under pressure to be released into the water for the generation of a primary pressure pulse in water, said chamber being formed of rigid wall structure and having an outlet port, movable valve means supported for movement between a closed position and a porting position, said valve means comprising: a. a pressure-retaining means, b. a stem portion extending from said pressure-retaining means and having a cross section much smaller than the cross-sectional size of said port, and c. a flared portion coupled to said stem portion and which increases in cross section in a direction away from said pressure-retaining means to a size much larger than the cross section of said stem portion, said pressure-retaining means sealing said port when said valve means is in said closed position, said stem and flared portions being located sequentially to pass through and beyond said port upon movement of said valve means to said porting position, and means for maintaining said valve means in said closed position for confining pressurized gas in said chamber and for allowing pressurized gas in said chamber to move said valve means to said porting position, said valve means upon movement away from said closed position toward said porting position, allowing gas under pressure to be released rapidly through said port and into the water to generate a pressure pulse in water, the rapid release of gas pressure into the water to generate the pressure pulse resulting in the formation of a bubble, said flared portion, upon movement through said port, reducing the size of the gas flow path through said port and then allowing the size of the gas flow path through said port to increase to allow additional gas to flow through said port into the resulting bubble formed to minimize secondary pressure pulses.
 6. In an acoustic source for generating pressure pulses in water for exploratory purposes, comprising: a chamber for receiving gas and holding gas under pressure to be released for the generation of a pressure pulse in water, said chamber being formed of rigid wall structure and having an outlet port, movable valve means supported for movement between a closed position and a porting position for closing and opening said outlet port, respectively, means for maintaining said valve means in its closed position for confining pressurized gas in said chamber and for allowing pressurized gas in said chamber to move said valve means to said porting position for releasing pressurized gas rapidly from said chamber by way of said port into the water to generate a pressure pulse in water, the rapid release of pressurized gas into the water to generate the pressure pulse resulting in the formation of a bubble, and means for returning said valve means to said closed position, the combination therewith of: gas release control means coupled to said valve means and supported to extend therefrom for controlling the releasE of gas through said port to reduce secondary pressure pulses, said gas release control means having a larger portion in cross section spaced from said valve means and a smaller portion in cross section located between said larger portion and said valve means, said valve means, upon movement to said porting position, causing first said smaller portion and then said larger portion to move through and beyond said port, said larger portion, upon movement within said port, decreasing the rate of gas flow through said port and then allowing the rate of gas flow through said port to be increased as it moves beyond said port whereby additional gas is allowed to flow through said port into the bubble to minimize secondary pressure pulses.
 7. In an acoustic source for generating acoustic pulses in water for marine seismic exploration operations, comprising: a chamber for receiving gas and holding gas under pressure to be released into the water for the generation of a pressure pulse, said chamber being formed of rigid wall structure to be immersed in water, said chamber having a first end and an outlet port, annularly shaped structure coupled to said wall structure at a position spaced from said first end, said outlet port extending through said annularly shaped structure, movable valve means formed of structure supported for movement between a closed position adjacent said annularly shaped structure and an open position for closing and opening said outlet port, respectively, said valve means preventing the release of pressurized gas from said chamber when said valve means is in said closed position, an electrical coil associated with said annularly shaped structure to form an electromagnet: a. for forming a magnetic holding force when electric current is applied to said coil for application of said force to said structure of said valve means for holding said valve means in said closed position against pressurized gas in said chamber, and b. responsive to decreased current flow for decreasing said holding force to allow pressurized gas in said chamber to move said valve means to said open position to release pressurized gas rapidly from said chamber by way of said outlet port for flow into the water to generate a pressure pulse, the rapid release of pressurized gas into the water to generate said pressure pulse resulting in the formation of a bubble, and means for returning said valve means to said closed position, the combination therewith of: gas release control means coupled to said valve means for controlling the release of gas through said port to reduce secondary pressure pulses, said gas release control means comprising: a stem portion extending from said valve means and having a cross section much smaller than the cross-sectional size of said port, and a flared portion coupled to said stem portion and which increases in cross section in a direction away from said valve means to a size much larger than the cross section of said stem portion, said stem and flared portions being located sequentially to pass through and beyond said port upon movement of said valve means to said porting position, said flared portion, upon movement within said port, reducing the size of the gas flow path through said port and then allowing the size of the gas flow path through said port to increase as it moves beyond said port to allow additional gas to flow through said port into the bubble formed to minimize secondary pressure pulses.
 8. In an acoustic source for generating pressure pulses in water for exploratory purposes, comprising: a chamber for receiving gas and holding gas under pressure to be released into the water for the generation of a pressure pulse, said chamber having an axial opening smaller in cross section than the cross-sectional area of said chamber in a plane perpendicular to the axis thereof, structure having lateral vent means formEd therethrough, valve means supported for movement within said structure between a closed position adjacent said opening and a porting position spaced from said opening, means for maintaining said valve means in said closed position for confining pressurized gas in said chamber and for allowing pressurized gas in said chamber to move said valve means to said porting position, the combination therewith of: gas release control means coupled to said valve means and supported to extend therefrom for controlling the release of gas to reduce secondary pressure pulses, said gas release control means having a larger portion in cross section spaced from said valve means and a smaller portion in cross section located between said larger portion and said valve means, said valve means, upon movement to said porting position, causing first said smaller portion and then said larger portion to move through and beyond said opening, said valve means, upon movement away from said closed position toward said porting position, allowing gas under pressure initially to be released rapidly through said opening and through said vent means into the water to generate a pressure pulse in water, the rapid release of pressurized gas into the water to generate the pressure pulse resulting in the formation of a bubble, and said larger portion, upon movement within said opening, decreasing the rate of gas flow through said opening and then allowing the rate of gas flow through said opening to be increased as it moves beyond said opening whereby additional gas is allowed to flow through said opening and through said vent means into the bubble to minimize secondary pressure pulses.
 9. The acoustic source of claim 8 wherein: said opening is formed through a member having a surface facing said valve means, said valve means having a surface facing said surface of said member and movable adjacent thereto upon movement of said valve means to said closed position, said member having rounded edges formed between said opening and said surface of said member facing said valve means.
 10. An acoustic source for generating acoustic pressure pulses in water for exploratory purposes while reducing secondary pressure pulses which occur following release of high pressure gas into water, comprising: a chamber for receiving gas and holding gas under pressure to be released into the water for the generation of a primary pressure pulse in water, said chamber being formed of rigid wall structure and having an outlet port, a valve member normally closing said outlet port and being movable away from said outlet port to an open position, and an enlarged member attached to and spaced from said valve member, said enlarged member passing through said outlet port upon movement of said valve member to said open position to decrease the rate of flow of gas through said port and to thereafter allow more of said gas to flow through said port into the bubble formed following the initial release of gas pressure to minimize secondary pressure pulses. 